Two microfiche appendices are part of this application. A first appendix, called Appendix I, includes 98 frames. A second appendix, called Appendix II includes 69 frames.
1. Field of the Invention
This invention concerns methods and apparatus for processing seismic data to display subterranean geologic formations, specifically complex formations. In particular the invention relates to computer implemented triangulation methods for generating representations of complex shapes form seismic data.
2. Description of the Prior Art
SeisWorks, a computer process of software of Landmark Graphics Corporation, allows the creation of single-valued horizon surfaces and of triangulated fault surfaces, but is mute regarding other surfaces of geologic interest such as saltdomes, stream channels, and lenses. The SeisWorks approach to fault surfaces fails to handle the more complex geologic shapes.
Landmark""s SeisWorks fault triangulation method is based on the Thiessen or Delaunay algorithm which requires that the fault be a single-valued surface in the triangulating coordinate system. To meet this condition in cases where a fault is multivalued with respect to the x,y plane, the present SeisWorks method begins with a determination of a natural coordinate system for any given set of segments. This system is such that the u,v coordinates lie in a plane which best fits the segment data, a condition which will usually result in the required single-valuedness.
However, for saltdomes, lenses, stream meanders, etc., there is no rotation of x,y,z for which the surface is single-valued, and the Thiessen approach must be applied piecemeal if indeed it is worth applying at all.
In reality a different approach is needed, and this approach can be supplied by Rib Technology, the creation of triangulated surfaces based on orderable sets of ribs, 3D polylines which are quasi parallel to their neighbors.
By combining this technology with appropriate workflows for gathering ribs (pseudo-fault segments), it is already possible to obtain triangulated surfaces of saltdomes and other complex shapes from SeisWorks. Moreover, the same concepts can be applied to fault triangulation with results that will be faster to obtain and superior in quality to those from the Thiessen method.
Rib Technology adds significantly to the surface production capabilities of SeisWorks with respect to complex shapes of geologic importance hitherto untreatable. It may totally supplant SeisWorks""present approach to the representation of fault surfaces because of its superior results and faster computation time. Furthermore it is capable to support horizon surface production in cases where the single-valued horizon surface assumption fails.
This same technology also enhances SeisWorks surface editing capability, which is presently an all-or-nothing proposition (if a fault segment is touched, the entire fault surface is invalidated and recomputed from scratch when next accessed), by enabling localized surface editing.
Additionally, by providing an ordering in one direction by rib index and in another by node index, this method leads directly to parametric coordinates and to useful surface representations other than triangulations such as smooth bi-cubic surface patches.